Optical waveguide devices are indispensable in various high technology industrial applications, and especially in telecommunications. In recent years, these devices, including planar waveguides, and two or three dimensional photonic crystals are being used increasingly in conjunction with conventional optical fibers. In particular, optical waveguide devices based on high refractive index contrast or high numerical aperture (NA) waveguides are advantageous and desirable in applications in which conventional optical fibers are also utilized. However, there are significant challenges in interfacing optical high NA waveguide devices, including chiral optical fiber devices, with conventional low index contrast optical fibers. Typically, at least two major obstacles must be dealt with: (1) the difference between the sizes of the optical waveguide device and the conventional fiber (especially with respect to the differences in core sizes), and (2) the difference between the NAs of the optical waveguide device and the conventional fiber. Failure to properly address these obstacles results in increased insertion losses and a decreased coupling coefficient at each interface.
For example, conventional optical fiber based optical couplers, such as shown in FIG. 6 (Prior Art) are typically configured by inserting standard optical fibers (used as input fibers) into a capillary tube comprised of a material with a refractive index lower than the cladding of the input fibers. There are a number of significant disadvantages to this approach. For example, a fiber cladding-capillary tube interface becomes a light guiding interface of a lower quality than interfaces inside standard optical fibers and, therefore, can be expected to introduce optical loss. Furthermore, the capillary tube must be fabricated using a costly fluorine-doped material, greatly increasing the expense of the coupler.
A commonly assigned U.S. Pat. No. 7,308,173, entitled “OPTICAL FIBER COUPLER WITH LOW LOSS AND HIGH COUPLING COEFFICIENT AND METHOD OF FABRICATION THEREOF”, which is hereby incorporated herein in its entirety, advantageously addressed all of the above issues by providing various embodiments of a novel optical fiber coupler capable of providing a low-loss, high-coupling coefficient interface between conventional optical fibers and optical waveguide devices.
Nevertheless, a number of challenges still remained. With the proliferation of optical devices with multiple waveguide interfaces (e.g., waveguide arrays), establishing low-loss high-accuracy connections to arrays of low or high NA waveguides often provide problematic, especially because the spacing between the waveguides is very small making coupling thereto all the more difficult. The commonly assigned U.S. Pat. No. 8,326,099, entitled “OPTICAL FIBER COUPLER ARRAY”, issued Dec. 4, 2012, which is hereby incorporated herein by reference in its entirety, addressed the above challenge by providing, in at least a portion of the embodiments thereof, an optical fiber coupler array that provides a high-coupling coefficient interface with high accuracy and easy alignment between an optical waveguide device having a plurality of closely spaced high NA waveguide interfaces, and a plurality of optical fibers each having low numerical apertures separated by at least a fiber diameter. While the '099 Patent already teaches the coupler, which is capable to independently control waveguide NAs and channel-to-channel spacing, it did not specifically address the full extent of configurability with respect to interfacing with plurality of optical fibers, and with respect to adaptability of specially configured exemplary embodiments of the novel optical fiber coupler array for high power laser applications.
It is important to note that the practice of coherent combining of multiple fiber lasers has been advantageously utilized in development of multi-kilowatt single mode laser sources for a variety of applications, including, but not limited to, directed energy sources for military and defense applications, for free-space optical communications, for materials processing, and in many more industrial, scientific and even medical applications.
Combining multiple individual laser sources, versus creating a single high power laser source, allows for more efficient thermal management, which is one of the most significant limiting factor in high power laser systems. In order to achieve a coherent combination of multiple laser sources, the optical phases of the laser sources being combined must be synchronized (or “phase locked”).
One of the known and commonly used approaches to accomplish passive phase locking, is to utilize the “Talbot effect”, which defines a distance at which a periodic pattern recreates itself while propagating in free space. Therefore, Talbot laser cavities are used to lock the phases of Individual laser sources or amplifiers. To achieve the Talbot effect, it is critical that the array of coupled waveguides has good spatial periodicity, and that the distance from the face of a waveguide array to a reflector is precisely selected and maintained. At present, different elements of a commonly used Talbot cavity are free-space optical elements, mechanically held at predefined locations, which makes it very difficult to maintain environmental stability.
Accordingly, it would be advantageous to provide various embodiments of an inventive PROFA-based optical fiber link component that may be configured and optimized to achieve highly desirable phase locking characteristics.